The objective of this proposal is to investigate the cellular processes that underlie the formation of synapses during development. Two related projects are proposed. The first involves the development of the synapses that form between dissociated rat sympathetic principal neurons in culture. The establishment of contact between growth cone and target neuron will be followed with Nomarski differential interference microscopy and the subsequent development of the contacts into synapses will be investigated with scanning and transmission electron microscopy. The order in which synaptic functions appear at forming synapses will be studied with morphological markers identified for these components. The morphological correlates of the onset of synaptic function will be determined by examining forming synapses after intracellular recording has established the presence of transmission. Previous studies of dissociated sympathetic neurons have shown that the transmitter choice of these neurons can be influenced by the environment. The second project involves a comparison of the development of the cholinergic sympathetic innervation of the eccrine sweat gland of the rat with that described for the cholinergic sympathetic neurons in culture.